Electrolytic process apparatus

ABSTRACT

Electrolytic process apparatus comprises a voltage source for electrically coupling to first and second electrodes, a detection circuit electrically coupled to the voltage source and a guard for providing a barrier between the first and second electrodes. The guard is arranged to permit current to travel within an electrolyte between the electrodes. The guard includes a guard conductor arranged to be electrically isolated from the electrodes. The guard conductor is arranged to be electrically coupled to the detection circuit such that the detection circuit can detect the presence of a current path between the guard conductor on the one hand and either electrode on the other hand.

BACKGROUND

1. Field

The present invention relates to electrolytic process apparatus. The present invention also relates to a guard for providing a barrier between first and second electrodes in an electrolytic process apparatus and to a guarded electrode for electrolytic process apparatus.

2. Background of the Invention

Electro deposition is a known electrolytic process for depositing a layer of material, such as a metal, to a target surface. According to one known technique, as shown in FIG. 1, an electro deposition apparatus 1000 includes a tank 1002 containing an electrolyte solution 1004. A target object 1008 is connected to a negative terminal 1012 of a power supply (not shown) thus forming a cathode. A source object 1006 is connected to a positive terminal 1010 of the power supply, thus forming an anode. Both the anode 1006 and cathode 1008 are immersed in the electrolyte solution 1004. The power supply supplies a direct current (dc) to the anode 1006, thereby charging the molecules dissolved in the electrolyte solution 1004. The dissolved metal ions in the electrolyte solution 1004 are attracted to and plate the surface of the cathode. This is known as electro deposition, as will be understood by a person skilled in the art. Sufficient dissolved metal ions in the electrolyte solution (as appropriate for the process) may allow inert anodes or secondary anodes to be used.

A known problem with electro deposition is that it can be difficult to obtain a uniform thickness of deposited material on the cathode. The geometry of the cathode can contribute to this problem. For example, if the cathode contains bores or relief profiles, it is possible that a fixed position anode may not cause the inside of the bore, for example, to be plated to a desirable thickness, uniformity or quality. In some cases the ions are attracted to external corners and protrusions rather than recesses. A known solution to this problem is to use multiple anodes and/or a specially shaped anode, known as a conforming anode, which matches a surface profile of the cathode. However, if the cathode is, for example, a one-off or rarely produced object, the cost of producing a conforming anode may not be justified. Also, the cost and time involved with either using multiple anodes or moving a single anode to different positions with respect to the cathode increases the cost associated with plating the cathode. As shown in FIG. 2, a known way of alleviating this problem is to use an auxiliary anode 1014, which is connected to the positive terminal 1016 of the power supply. The auxiliary anode, or guarded anode, can be manually held and used to ‘touch up’ areas such as recesses or bores which require special attention.

A problem with using an auxiliary anode is that, should the anode touch the cathode, a spark or sparks may jump between the anode and cathode, which can burn the cathode. This is known as arcing. In some cases, the burn caused by arcing occurring between the anode and cathode can structurally compromise the cathode. For example, should the cathode be an aeroplane landing gear, which is purposefully made from thin and lightweight materials to keep the weight of the landing gear to a minimum, such a burn due to arcing could render the landing gear unusable. Therefore, a single instance of contact between the anode and cathode has the potential to destroy an expensive object, such as a landing gear, that forms the cathode.

As shown in FIG. 3, a known solution to this problem is to use a perforated guard 1100 which is placed over the auxiliary anode. The guard is formed from an insulating material, such as plastic mesh, and forms a barrier between the auxiliary anode and the cathode. The guard material permits ions to pass from the anode, through the perforations, to the cathode and thereby plate the cathode. Whilst the insulating guard stops the anode from contacting the cathode, after time, the guard may wear and therefore permit the anode to touch the cathode, thereby permitting arcing to occur which can damage the cathode. In addition, the coverage of the guard material may still allow contact between the anode and corners or, alternatively, edges of the cathode.

SUMMARY

According to a first aspect of the present invention there is provided electrolytic process apparatus comprising a voltage source arranged to be electrically coupled to first and second electrodes, a detection circuit electrically coupled to the voltage source and a guard for providing a barrier between the first and second electrodes, the guard being arranged to permit current to travel within an electrolyte between the electrodes, wherein the guard includes a guard conductor arranged to be electrically isolated from the electrodes and arranged to be electrically coupled to the detection circuit such that the detection circuit can detect the presence of a current path between the guard conductor on the one hand and an electrode on the other hand.

Thus the guard provides a physical barrier between the electrodes such that they can be brought close together during the electrolytic process without the issue of the electrodes touching one another, which can cause a spark that may damage one or both of the electrodes. The guard conductor is arranged to be electrically coupled to a monitoring circuit and is substantially electrically isolated from both the electrodes, for example by an insulating coating. Thus, a voltage can be applied to the guard conductor by the monitoring circuit, or a separate supply voltage, and, unless the means of insulation becomes damaged, substantially no current path exists between the guard conductor and an electrode. Should the means of insulation become damaged, so as to expose a part of the guard conductor, contact, or near contact, between the exposed part and an electrode will create a current path therebetween which can be detected by the monitoring circuit. This current path may indicate that the guard needs replacing.

The detection circuit may be arranged to transmit a signal, upon detecting the presence of the current path, operable to deactivate the voltage source.

Thus, the current path between the guard conductor and an electrode can be used as a trigger to cause the monitoring circuit to cause the voltage supply to shut off. This can prevent damage to an electrode caused by arcing occurring between the electrodes.

The detection circuit may include a first detector arranged to monitor the difference in an electrical characteristic between the guard and first electrode and/or a second detector arranged to monitor the difference in an electrical characteristic between the guard and second electrode and/or a third detector arranged to monitor the difference in an electrical characteristic between the electrodes. The electrical characteristic may be one or more of voltage, resistance or current.

The detection circuit may include a switch associated with a voltage detector, the voltage detector being arranged to generate a signal operative to open the switch in response to the monitored voltage difference exceeding a predefined threshold, such that upon the switch opening the voltage source is switched off.

The guard may include an insulating coating provided over all surfaces of the guard conductor except those parts by which the guard conductor is arranged to be electrically coupled to the monitoring circuit.

Thus, the guard conductor may be electrically insulated from the electrodes by way of an electrically insulating coating, for example PVC. It should be understood that “electrically insulated” means that a closed circuit may not be formed between the guard conductor and electrodes while the means of insulating the guard conductor from the electrodes is present and functioning.

The guard may be arranged to enclose a part of the first electrode. The guard conductor may be coiled around the first electrode.

Thus, by enclosing the first electrode the guard may form a barrier around the part of the electrode meaning that a physical barrier exists between the electrodes in a plurality of orientations of the first electrode.

The guard may include an insulating bracket arranged to fixedly space the conductor from the first electrode.

Thus, by spacing the guard from the anode, in some embodiments a greater quantity of the electrolyte solution will be in contact with electrode, which may improve the electrolytic process compared with if the guard were directly in contact with a part of the electrode.

The first electrode may be an anode and the second electrode a cathode. Alternatively, the first electrode may be a cathode and the second electrode an anode. The arrangement is determined by the process required (for example, plating uses the first electrode as an anode, anodising uses the first electrode as a cathode).

The detection circuit may have one or more set points, the set points being either fixed value or arranged to be automatically adjusted in accordance with the voltage source output.

According to a second aspect of the present invention, there is provided a guard for providing a barrier between first and second electrodes of an electrolytic process apparatus according to the first aspect of the invention, the guard being arranged to permit current to travel within an electrolyte between the electrodes, wherein the guard includes a guard conductor arranged to be electrically isolated from the electrodes.

The guard may include an insulating coating provided over all surfaces of the guard conductor except those parts by which the guard conductor is arranged to be electrically coupled to a monitoring circuit.

The guard may be arranged to enclose a part of the first electrode and/or may be coiled around the first electrode. Optionally or in addition, the guard may include an insulating bracket arranged to fixedly space the conductor from the first electrode.

DRAWINGS

Embodiments of the present invention will now be described, by way of example only, with reference to the accompanying drawings, in which:

FIG. 1 is a schematic diagram of known electro deposition apparatus;

FIG. 2 is a partial view of a known auxiliary anode being used to “touch-up” a cathode;

FIG. 3 is a known guarded auxiliary anode;

FIG. 4 shows a cross-sectional view of a guarded auxiliary anode according to an embodiment of the invention, including a guard according to an embodiment of the present invention;

FIG. 5 shows a partial cross-sectional view of a guard for an electro deposition anode according to an embodiment of the present invention;

FIG. 6 shows a block diagram of electrolysis apparatus according to an embodiment of the invention; and

FIG. 7 shows a schematic diagram of electrolysis apparatus including detail of a detection circuit according to an embodiment of the present invention.

DETAILED DESCRIPTION

The following description relates to plating applications (where the work is connected to the negative terminal of the power supply). However, it is to be understood that the apparatus can be used in a wide range of electrolytic processes such as Plating, Anodising, Etching, Electro cleaning, Electro polishing, Electrophoretic painting, Electro colour, etc . . .

“The Work” (the part to be treated) can be either negative (in the case of plating applications) or positive in the case of anodising or as required by the particular process. In the case of some applications, such as electro colour, a mixture of AC & DC can also be used.

Referring to FIG. 4 a guarded auxiliary anode 10 is shown according to an embodiment of the invention. The guarded auxiliary anode 10 includes an anode 1014 arranged to be electrically coupled to the positive terminal 1010 of a direct current (DC) power supply, such as a rectifier, via an electrically insulated connecting wire 1011. Suitable materials for the anode 1014 include stainless steel and Cadmium, although other materials may also be used as is necessary for the process in question. It will be understood that the anode 1014 is an electrode.

The guarded auxiliary anode 10 includes a guard 20. The guard 20 is arranged to provide a physical barrier between the anode 1014 and a cathode (not shown) during an electro deposition process and is arranged so as to permit current to travel within an electrolyte solution between the anode 1014 and a cathode. It will be understood that the cathode is an electrode. The guard 20 thus permits or allows free circulation of the plating solution through the guard 20, thus allowing the free flow of the dissolved metal ions in the plating solution from the anode, through the guard to the cathode.

The auxiliary anodes, cathodes and associated guards can be any shape or size, specifically designed to serve one or a number of components as necessary.

In the illustrated embodiment the guard 20 is arranged to be connected to an anode 1014 and arranged to surround a part of the anode 1014. However, in other embodiments the guard 20 may be arranged to form a physical barrier between the anode 1014 and a cathode without surrounding or enclosing the anode 1014. For example, in other embodiments the guard 20 may be arranged to be attached to a further structure, such as a part of the tank containing the electrolyte solution or the cathode, so as to provide a physical barrier between the anode 1014 and cathode. Also, it will be appreciated that the guard 20 can be arranged to be connected to the anode 1014 without enclosing it yet still be arranged to provide a barrier between the anode 1014 and cathode. For example, the guard 20 could be arranged to be located at one side of the anode 1014. It will be appreciated that it is advantageous for the guard 20 to be arranged to be connected to the anode 1014 because if the guard 20 is attached to the anode 1014 it will generally move with the anode 1014 as the anode is manipulated by a user in use. In some embodiments, the guard may be arranged to surround all or at least some of a cathode.

The guard 20 comprises a conductive core, for example stainless steel wire, with an electrically insulating coating, for example PVC, which is preferably provided over substantially all exposed surfaces of the conductive core. The conductive core forms a guard conductor which enables electric current to travel though the guard 20. The guard conductor provided within the guard 20 is arranged to be electrically coupled to a power supply via one or more insulating cables 24 to a short-circuit detection system (not shown).

In the illustrated embodiment, the guard 20 is configured to form a conductive metal spiral around the anode to prevent contact between the anode 1014 and a cathode. However, whilst in the illustrated embodiment the guard 20 includes a single guard conductor, in other embodiments the guard 20 may include a plurality of guard conductors. Where the guard 20 includes a plurality of guard conductors, the guard conductors may be arranged in a cage-like formation arranged to enclose a part of an anode 1014. The cage-like formation may include one or more interconnecting elements which may be an electrically insulating material, such as a plastics material, or may, in some embodiments, comprise guard conductors having an insulating coating. In another embodiment the guard conductor may be a perforated tube, mesh tube, or the like, arranged to substantially enclose a part of the anode 1014. It will be appreciated that the cage-like formation and perforated guard conductor permits electrolyte to be present within the spaces between elements, or the holes formed through, of the guard and thus permit ions to travel within an electrolyte solution between the anode 1014 and a cathode.

In the illustrated embodiment the guard 20 is held in place relative to the anode 1014 by brackets 14 a and 14 b that are substantially fixed or fixable at a location on the anode 1014. The brackets 14 a and 14 b are connected to the guard 20 so as to maintain the guard 20 at a substantially fixed position relative to the anode 1014. In this example, the brackets 14 a and 14 b comprise an insulating material, such as a plastics material, for example PVC. The brackets 14 a and 14 b may be fixed or fixable to the anode 1014 by way of a cooperating surface profile forming an interlock, mechanical fixing means, such as a screw, or any other suitable fixing means that maintains the brackets 14 a and 14 b at a substantially fixed position on the anode 1014. The short distance between the anode 1014 and the guard 20 also reduces the potential for corners/edges on the cathode from touching the anode. The guard is supported at this short distance from the anode using supports at each end of the anode, together with the option for additional supports along the length of the anode (the requirement for additional supports along the length of the anode is dependent upon the length of the anode and the rigidity of guard material). In the illustrated embodiment the brackets 14 a and 14 b are cuboid in shape, having an inner bore arranged to receive a part of the anode 1014. In other embodiments a bracket could be made from a material that shrinks to affix itself to the anode 1014 with applied heat. It is advantageous that when a bracket is arranged to be fixed to the anode 1014 in this manner that the bracket comprises a material having a reasonable coefficient of friction, to reduce the likelihood of the bracket sliding relative to the anode 1014. The anode 1014 may be provided with a handle 12 formed of an electrically insulating material, which in use may be held by a user whilst manipulating the guarded anode 10. The handle 12 also supports the guard 20.

Although brackets 14 a and 14 b are provided in the illustrated embodiment, it will be appreciated that in other embodiments the guarded anode 10 may include other suitable means for maintaining the guard 20 at a substantially fixed position relative to the anode 1014. in another embodiment, the guard may be closely associated with the anode 1014, for example wound around the anode 1014 and insulated there from by the insulating coating. In another embodiment, the guard 20 may be arranged to be screwed or bonded to the anode 1014 or attached by another suitable fixing means.

Referring to FIG. 6, electro deposition apparatus 50 is shown according to an embodiment of the invention. The apparatus 50 includes a guarded anode 10 according to an embodiment of the present invention that may be used to electroplate a cathode 1008. The guarded anode 10 and cathode 1008 are located within a tank of electrolyte solution (not shown). The apparatus further includes a power supply 34 and a detection circuit 36 for detecting a short circuit between the guard conductor within the guard 20, on the one hand, and the anode 1014 and/or cathode 1008, on the other. The anode 1014 of the guarded anode 10 is coupled to the positive terminal 34 a of the power supply 34 via an electrically insulated connecting wire 1011. The cathode 1008 is coupled to the negative terminal 34 b of the power supply 34 via an electrically insulated connecting wire 1013.

The detection circuit 36 includes an anode terminal 36 a coupled to the positive terminal 34 a of the power supply 34 via an electrically insulated connecting wire 40. The detection circuit 36 also includes a cathode terminal 36 b coupled to the negative terminal 34 b of the power supply 34 via an electrically insulated connecting wire 38. The detection circuit 36 further includes a guard terminal 36 c coupled to the guard conductor within the guard 20 via an electrically insulated connecting wire 24.

The potential difference between the positive terminal 34 a and negative terminal 34 b of the power supply in this example is 6V DC, although it will be appreciated that other voltages can be used depending on the process. The guard 20 is part of an open circuit that is made when a short or near short occurs between the guard conductor within the guard 20, on the one hand, and the anode 1014 and/or cathode 1008, on the other. The detection circuit is arranged to detect the presence of a short or near short circuit and perform an output based on the detection, such as cutting the power supplied by the power supply 34 and/or causing a warning signal to be generated. The detection circuit 36 is arranged to detect a short or near short circuit occurring between the guard conductor and anode 1014 or cathode 1008, whilst ensuring that during detection there is no significant current flow through the guard (i.e. the current flowing through the guard is limited to a few mA) so as to limit the possibility of damage occurring to, for example, the cathode 1008.

Referring to FIG. 7, a detection circuit 36 according to an embodiment of the invention is shown. The detection circuit 36 and power supply 34 are implemented as a common unit 34/36. The guarded anode 10 and cathode 1008 are connected to the power supply 34 as described with reference to FIG. 6 so as to provide, in this example, a potential difference between them of 6V DC in this example. The guard 20 is coupled to the anode terminal of the power supply via a resistor R1 and is coupled to the cathode terminal of the power supply via a resistor R2. The values chosen for R1 and R2 should be large enough such that at the full voltage of the DC power supply 34 only a very small current, for example 5 mA, can flow through either of the resistors. It will be appreciated that the resistors R1 and R2 are configured in the circuit to form a potential divider, with the guard being connected between them. As such, it is preferable that the value for R1 is generally equal to that for R2, such that the guard 20 has a potential the value of which is half way between the anode 1014 and cathode 1008.

A voltage detector V1 is provided in parallel with R1 between the guard 20 and anode 1014 such that the voltage of the guard conductor relative to the anode 1014 can be measured. A voltage detector V2 is provided in parallel with R2 between the guard 20 and cathode 1008 such that the voltage of the guard conductor relative to the cathode 1008 can be measured. A short circuit or near short circuit can be determined when the guard conductor voltage gets close to the voltage of either the anode 1014 or cathode 1008. In this example the potential difference between the anode 1014 and cathode 1008 is 6V, meaning that if the values of R1 and R2 are substantially the same then a 3V potential difference will exist between the guard 20 and anode 1014. Similarly, a 3V potential difference will exist between the guard 20 and cathode 1008. The voltage detectors V1 and V2 are set to 2.5V. If the voltage detector V1 detects that the potential difference between its measuring nodes (i.e. a wire coupled to the anode 1014 and a wire coupled to the guard conductor of the guard 20) it causes a trip condition. Voltage detector V2 provides the same function between the guard 20 and cathode 1008. The illustrated example also includes a third voltage detector V3 provided in parallel with resistors R1 and R2 and arranged to measure the anode to cathode voltage. It will be appreciated that other values for the voltage detectors can be used. In some embodiments, the detectors may have variable set points which automatically adjust to the output voltage of the rectifier. Thus, as the output voltage is adjusted the voltage detectors can automatically adjust to suit. In some embodiments the monitoring circuit may instead or in addition monitor one or more circuit conditions other than voltage, for example current and/or resistance. The monitoring circuit may include any number and combination of detectors. Many suitable monitoring arrangements will be apparent to the skilled person for detecting a short circuit, or near short circuit, between the guard conductor on the one hand and the cathode and/or anode on the other hand.

Voltage detectors V1 to V3 control respective relays RV1 to RV3 in a power control circuit for the power supply 34. Relays RV1 to RV3 are provided in series such that if any are “open” the power supply 34 is in an “off” state. If each of RV1 to RV3 is “closed” then the power supply 34 is in an “on” state. In some embodiments voltage detector V3 and associated relay RV3 are not included in the detection circuit 36 and in other embodiments only one of voltage detector V1 and V2 (and their associated relay) are provided, depending upon which type of short circuit the detection circuit 36 is arranged to detect. It should be noted that a timer override circuit is included in the present example because the DC power supply 34 is also used as the voltage source for the guard conductor in the guard 20. The timer is set to an appropriate time, for example 2 seconds, to allow the DC power supply 34 to reach the required set point. Prior to this time, the timer will stop the voltage detectors from causing a trip condition which causes the power supply 34 to be turned off. In other arrangements the timer may not be required.

As noted above, the present example includes an optional voltage detector V3 and associated relay RV3 arranged to measure the anode to cathode voltage, The DC power supply 34 includes a fast acting current limiting circuit which causes the output voltage of the DC power supply 34 to drop if the supplied current reaches a set point. It will be appreciated that the current set point may be determined by the surface area of the cathode and can be any value appropriate for the process, having due regard to the capability of the DC power supply and the current carrying capacity of the anode, cathode and cabling. By measuring the voltage between the anode and cathode, if the voltage goes too low, in this example below 5V, this indicates that there is a short or near short circuit between the anode and cathode, which will cause a trip condition. In some embodiments the trip circuits may made to latch (not shown), which will allow indication to be provided via lamps as to the cause of the trip.

In use the guarded anode 10 can be utilised to “touch up” an area of a cathode 1008 where, for example, the layer of plated material is not to a satisfactory level. The guarded anode 10 can be manipulated within the electrolyte solution so as to be brought near to the area which requires localised plating. In the present example which concerns plating, the voltage supplied by the DC power supply 34 causes ions to flow from the anode 1014 to be deposited on the cathode 1008. If the user inadvertently touches the cathode 1008 with the guarded anode 10 the guard 20 prevents the anode 1014 from touching the cathode 1008 thereby preventing arcing from occurring which has the potential to damage the cathode object 1008.

If contact between the guard 20 and cathode 1008 causes damage to the insulating coating 12 so as to expose a part of the guard conductor, contact between the exposed guard conductor 16 and the cathode 1008 will cause ‘controlled conduction’ to occur there between. However, the detection circuit is arranged such that controlled conduction supplies a current of a few milliamps (mA) which is unlikely to burn and damage the cathode 1008.

In the illustrated embodiment the output provided by the detection circuit 36 in response to detecting a short circuit or near short circuit is a cut off signal to turn off the DC power supply 34. The action of the rectifier cutting the power supply to the anode 1014 may serve to notify the user that the insulating layer 12 on the guard 20 has worn and thus the guard needs replacing. The guard conductor therefore acts as a “fail safe” arranged to prevent the guard 20 from wearing sufficiently to permit the anode 1004 to contact the cathode 1008 by allowing a small current to flow through the guard conductor upon a short circuit occurring, which triggers an output. In other embodiments, the output can be or further include some other means of indicating that the guard 20 has worn, such as an audible alarm or the like.

The guard, guarded electrode and electrolytic process apparatus according to embodiments of the present invention are suitable for use in various electrolytic processes, such as electroplating, anodising, etching, electro cleaning electro polishing, electrophretic, and electro colour, and is particularly suited to use in electroplating applications with high value objects that may be damaged easily by arcing occurring between an auxiliary anode and cathode, such as aeroplane parts. When the electrolytic process apparatus is electro deposition apparatus it is preferable that the guard is mounted on and provides a barrier around the anode, as it is the anode which is used as a “wand” to electroplate the cathode from different orientations and is generally the smaller of the two. When the electrolytic process apparatus is anodising apparatus, it is preferable that the guard is mounted on and provides a barrier around the cathode. 

1-19. (canceled)
 20. Electrolytic process apparatus comprising a voltage source arranged to be electrically coupled to first and second electrodes, a detection circuit electrically coupled to the voltage source and a guard for providing a barrier between the first and second electrodes, the guard being arranged to permit current to travel within an electrolyte between the electrodes, wherein the guard includes a guard conductor arranged to be electrically isolated from the electrodes and arranged to be electrically coupled to the detection circuit such that the detection circuit can detect the presence of a current path between the guard conductor on the one hand and an electrode on the other hand.
 21. Electrolytic process apparatus according to claim 20, wherein the detection circuit is arranged to transmit a signal, upon detecting the presence of the current path, operable to deactivate the voltage source.
 22. Electrolytic process apparatus according to claim 20, wherein the detection circuit includes a first detector arranged to monitor the difference in an electrical characteristic between the guard and first electrode.
 23. Electrolytic process apparatus according to claim 20, wherein the detection circuit includes a second detector arranged to monitor the difference in an electrical characteristic between the guard and second electrode.
 24. Electrolytic process apparatus according to claim 20, wherein the detection circuit includes a third detector arranged to monitor the difference in an electrical characteristic between the electrodes
 25. Electrolytic process apparatus according to claim 22, wherein the detection circuit includes a switch associated with a voltage detector, the voltage detector being arranged to generate a signal operative to open the switch in response to the monitored voltage difference exceeding a predefined threshold, such that upon the switch opening the voltage source is switched off.
 26. Electrolytic process apparatus according to claim 20, wherein the guard includes an insulating coating provided over all surfaces of the guard conductor except those parts by which the guard conductor is arranged to be electrically coupled to the monitoring circuit.
 27. Electrolytic process apparatus according to claim 20, wherein the guard is arranged to enclose a part of the first electrode.
 28. Electrolytic process apparatus according to claim 20, wherein the guard conductor is coiled around the first electrode.
 29. Electrolytic process apparatus according to claim 20, wherein the guard includes an insulating bracket arranged to fixedly space the conductor from the first electrode.
 30. Electrolytic process apparatus according to claim 22, wherein the deletion circuit electrical characteristic is one or more of voltage, resistance or current.
 31. Electrolytic process apparatus according to claim 20, wherein the detection circuit has one or more set points, the set points being either fixed value or arranged to be automatically adjusted in accordance with the voltage source output.
 32. A guard for providing a barrier between first and second electrodes of an electrolytic process apparatus according to claim 20, the guard being arranged to permit current to travel within an electrolyte between the electrodes, wherein the guard includes a guard conductor arranged to be electrically isolated from the electrodes.
 33. A guard according to claim 32, wherein the guard includes an insulating coating provided over all surfaces of the guard conductor except those parts by which the guard conductor is arranged to be electrically coupled to a monitoring circuit.
 34. A guard according to claim 32, wherein the guard is arranged to enclose a part of the first electrode.
 35. A guard according to claim 32, wherein the guard conductor is coiled around the first electrode.
 36. A guard according to claim 32, wherein the guard includes an insulating bracket arranged to fixedly space the conductor from the first electrode. 